Implantable Photonic Neural Probes with Out-of-Plane Focusing Grating Emitters

We have designed, fabricated, and characterized implantable silicon neuralprobes with nanophotonic grating emitters that focus the emitted light at aspecified distance above the surface of the probe for spatially preciseoptogenetic targeting of neurons. Using the holographic principle, we designedgratings for wavelengths of 488 and 594 nm, targeting the excitation spectra ofthe optogenetic actuators Channelrhodopsin-2 and Chrimson, respectively. Themeasured optical emission pattern of these emitters in non-scattering mediumand tissue matched well with simulations. To our knowledge, this is the firstreport of focused spots with the size scale of a neuron soma in brain tissueformed from implantable neural probes.